ORIGINAL: proptop
Slightly larger, with less pitch...hmmm...where have we heard that before...D-U? Dar?
Not only that but Webra say 30 minutes right at the 4-2 stroke break point.
It's strange though, from the description of the problem given by fc911c I would have said it was a ringed engine but going by that Webra site all GT's are ABN.